The present invention relates to an improved device and method for determining ultraviolet or other radiation exposure from the sun or other sources.
The harmful effects of exposing human and other mammalian skin to the ultraviolet portion of the radiation spectrum has long been known and documented. The harmful rays have been identified as being the spectral range from 290 to 320 nanometers, a region which is outside of the perceptual range of the human eye. The effects of ultraviolet exposure remain largely unpredictable despite recent advances in radiation detection technology, such as the ultraviolet index, because local anomalies in the atmosphere vary the inherent filtering potential in this spectral region. This filtering action depends upon a number of factors including the angle of incidence of the sun""s rays, the atmospheric thickness, a person""s altitude, cloud cover, and pollution.
Historically people have protected themselves from ultraviolet exposure by using lotions which contain ultraviolet filters. These lotions typically allow the so-called xe2x80x9ctanningxe2x80x9d radiation, wavelengths from about 320 to 400 nanometers, to penetrate while absorbing burning radiation, wavelengths shorter than 320 nanometers. However, these lotions offer only a fixed degree of protection by effecting a fixed degree of filtration. The degree of filtration cannot be typically be altered except by the purchase of another lotion with more or less filtration. Thus, the person desiring to adequately protect themselves from exposure to ultraviolet radiation must first determine the intensity of ultraviolet radiation emitted at their location. Although the ultraviolet index is useful in this determination, it is not a precise determinant of local ultraviolet radiation intensity. Clearly, an inexpensive ultraviolet dosimeter would be valuable to humans and other ultraviolet radiation sensitive mammals subject to ultraviolet radiation exposure.
There are a number of ultraviolet radiation dosimeters on the market and in the literature. These devices fall into two broad categories: electronic and chemical. The electronic devices typically contain a detecting device, usually equipped with appropriate filters to screen out unwanted electromagnetic radiation, and an amplifier, an electronic integrator, and display. Although such devices can be reasonably accurate, they are inherently complex, considering the electronic manipulation they must perform in order to display the desired result. Despite the tremendous advances in electronics, these devices remain relatively expensive and are typically beyond a price the public is willing to pay for the information the device generates. Furthermore, these electronic devices are subject to failure and damage due to misuse and inherent flaws.
The chemical devices typically undergo a reversible or irreversible color change initiated by incident ultraviolet radiation. These chemicals are designed to change structurally or chemically react when exposed to incident ultraviolet radiation. These chemicals, having been custom designed for a particular use, are not typically easy to manufacture, may exhibit long term harmful effects if they contact mammalian tissue, are difficult to calibrate, and cannot easily be altered to account for the ultraviolet susceptibility of different individualsxe2x80x94typically fair-skinned individuals are more likely to experience tissue damage due to a given dose of ultraviolet radiation than are dark-skinned individuals. These devices may also require matching to particular reference colors in order to establish ultraviolet radiation exposure and thus are flawed due to the inherent differences in individuals"" color-matching abilities.
Furthermore, the present inventions are described as having sensitivity only in the context of ultraviolet radiation as emitted by the sun, whereas the general nature of the invention described below allows it to be easily adapted to any radiation, such as X-Rays and Beta emissions, which will initiate the chemical reactions described therein.
The present invention overcomes the problems inherent in ultraviolet radiation dosimeter devices presently on the market or described in the literature by incorporating a simple, easily controlled chemical reaction of well known, inexpensive common chemicals which have minimal harmful properties. Generally, the invention comprises a device that permits ultraviolet radiation to penetrate and convert a mixture to change color to provide an indication that ultraviolet radiation has impinged the device. In a presently preferred embodiment, the mixture comprises iodide, Ixe2x88x92, which is converted to Iodine, preferably utilizing thiosulfate to convert iodine back to iodide, such that when the thiosulfate is depleted the iodine is complexed with starch to form a characteristically brown-colored starch-complexed iodine.
In the preferred embodiment, the rate at which the starch-complexed iodine is formed is adjusted by the amount of thiosulfate present. Thus, the time for coloration of an otherwise clear, typically, water-based solution can be extended by the addition of thiosulfate. In the preferred embodiment, potassium iodide is mixed with cornstarch, and preferably sodium thiosulfate. The preferred embodiment of the solution gives an approximately 8 Normal solution of potassium iodide in a 5% by mass solution of corn starch to which sufficient sodium thiosulfate is added to remove any non-ionic iodine, typically less than 10 micrograms sodium thiosulfate per 50 ml water herein called the solution. In the preferred embodiment of the device, this solution is optionally mixed with equal parts of liquid latex or other water-dispersed, curable, polymeric agent. The uncured polymeric agent disperses within the solution and when cured forms a matrix which inhibits the evaporation of water while allowing the transmission of ultraviolet radiation. Optionally, in a preferred embodiment approximately 2% by weight of Calcium chloride is added as a humidicant to retain and stabilize the moisture content of the cured material as described below. Other humidicants may be added to achieve the same purpose.
When the mixture is applied to a suitable strip of paper, polymer or other suitable surface, including skin, allowed to cure, and exposed to ultraviolet radiation, it gradually darkens to a brown hue. The rate of darkening is controlled by the amount of thiosulfate added to the solution. The rate of darkening can be adjusted for differences in exposure tolerance exhibited by individuals with varied skin susceptibility. Furthermore, the cured material may be applied to a surface which may incorporate calibrated brown hue references to establish the degree of ultraviolet exposure by simple matching of hue rather than color. Additionally, a humidicant may be added to the solution in order to enhance retention of water in the solution. Other advantages of the invention will become apparent from a perusal of the following detailed description of presently preferred embodiments taken in connection with the drawings which illustrate various carrier mechanisms for use of the invention.